A variety of conveyor roller systems have been designed and utilized. A large variety of known conveyor systems comprise a continuous belt or conveyor medium which travels over a series of conveyor rollers.
Early conveyor roller systems utilized at least one conveyor drive roller which was driven by an electric motor positioned outside of, and connected to, the conveyor drive roller typically via a chain or rubber belt, and often with an external gear assembly positioned between the motor and the conveyor roller. The conveyor drive roller thereby translated the rotational movement of the electric motor to linear movement of the conveyor medium. The main disadvantage of these early designs, which are still utilized today, is that they take up a lot of space. However, the exposed moving parts also pose a hazard to workers, especially the external gear assembly and chain from the external gear assembly to the conveyor roller, which output high levels of torque, as compared to the motor on its own. The exposed moving parts also pick up debris which damages the conveyor roller system.
In later conveyor roller systems, the electric motor was arranged within the conveyor drive roller to provide a more compact conveyor roller system as taught, for example, in U.S. Pat. No. 1,725,740, to Schulte. One problem with these types of prior motorized conveyor drive rollers is that the internal motor generates heat which is confined to a small space inside the roller tube or cylinder. The heat is generated as a function of the current flowing through the electric motor windings. Thus larger electric motors required to provide more powerful conveyor drive rollers typically generate more heat. If the heat is not adequately dissipated or controlled, it will lead to overheating. Overheating is the most common failure mechanism for an electric motor, and can lead to a) failure of the winding-isolation, which results in a short-circuit and possibly burnout of the motor, b) failure of the bearings, resulting in a jammed motor, and degradation of the magnets, leading to reduced performance. Overheating can also cause damage to the internal parts of the conveyor drive roller. Either failure mode leads to costly repairs and down time.
Accordingly, in the context of motors and motor only conveyor drive rollers there have been developments for cooling the motor windings, as disclosed in for example, U.S. Pat. Nos. 3,188,833, 4,728,840, 7,329,215, 7,362,016, and 7,543,700.
U.S. Pat. Nos. 5,088,596 and 7,510,073, represent examples of even more advanced conveyor drive rollers, which include an internal electric motor and gear assembly for engaging and rotating the roller tube or cylinder. Conveyor roller systems having conveyor drive rollers which are driven by motor and gear combinations, contained entirely within the conveyor drive roller itself, are of particular utility in many applications. One of the benefits of these types of conveyor drive rollers is that for a given power rating, the internal gear assembly permits use of a smaller electric motor, which results in less heat generation as compared to a similarly sized and power rated motor only conveyor drive roller. The use of an internal lubricant also assists with heat dispersal and dissipation. However, the internal motor and gear assembly system also makes for a compact, space saving installation. Furthermore, the linear arrangement of the motor and gear assembly within the conveyor drive roller means that the transmission of power from the motor to the roller is carried out more directly resulting in higher levels of efficiency than is possible in conventional conveyor roller systems where the motor is positioned externally to the conveyor drive roller, especially where the axis of rotation of the rotor is at a 90° angle to the axis of rotation of the roller. The internal motor and gear assembly combination also largely eliminates the risk of accident caused by contact with employees. Furthermore, it eliminates contamination of the motor/gear drive from dust and debris in the environment in which it is running, thereby greatly reducing maintenance, and the likelihood of failure, all of which results in less down time for the conveyor system. All of these factors make the use of such conveyor drive rollers particularly useful and desirable.
U.S. Pat. Nos. 7,806,252 and 8,292,064 represent an example of another conveyor drive roller, which includes an external electric motor with means to connect to an internal gear assembly for engaging and rotating the roller tube or cylinder. This latter example addresses a need for a conveyor having the benefits of internal gearing while providing an easily replaceable external motor to minimize cost and down time in the event of a failure of the electric motor.
However, a problem has been discovered with conveyor drive rollers with an internal gear assembly in that as the size of the conveyor drive roller is scaled up the heat generated increases to the point that the internal liquid lubricant begins to degrade and lose its viscosity, which can lead to premature failure. In such geared conveyor drive rollers the majority of the heat is generated by the rolling/scraping action of the gear assembly, and not the electric motor.
Other prior art patents of general interest in the field of conveyor roller devices include U.S. Pat. Nos. 6,250,376, 6,523,775, 6,683,284, and 7,097,605.
Therefore, there is a continuing need for improvement in the design of motorized conveyor drive rollers.